package com.xkdx.caipiao.util;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * Base64编码工具类
 */
public class Base64 {
        private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

        public static String encode(byte[] data) {
                int start = 0;
                int len = data.length;
                StringBuffer buf = new StringBuffer(data.length * 3 / 2);

                int end = len - 3;
                int i = start;
                int n = 0;

                while (i <= end) {
                        int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 0x0ff) << 8) | (((int) data[i + 2]) & 0x0ff);

                        buf.append(legalChars[(d >> 18) & 63]);
                        buf.append(legalChars[(d >> 12) & 63]);
                        buf.append(legalChars[(d >> 6) & 63]);
                        buf.append(legalChars[d & 63]);

                        i += 3;

                        if (n++ >= 14) {
                                n = 0;
                                buf.append(" ");
                        }
                }

                if (i == start + len - 2) {
                        int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 255) << 8);

                        buf.append(legalChars[(d >> 18) & 63]);
                        buf.append(legalChars[(d >> 12) & 63]);
                        buf.append(legalChars[(d >> 6) & 63]);
                        buf.append("=");
                } else if (i == start + len - 1) {
                        int d = (((int) data[i]) & 0x0ff) << 16;

                        buf.append(legalChars[(d >> 18) & 63]);
                        buf.append(legalChars[(d >> 12) & 63]);
                        buf.append("==");
                }

                return buf.toString();
        }

        private static int decode(char c) {
                if (c >= 'A' && c <= 'Z')
                        return ((int) c) - 65;
                else if (c >= 'a' && c <= 'z')
                        return ((int) c) - 97 + 26;
                else if (c >= '0' && c <= '9')
                        return ((int) c) - 48 + 26 + 26;
                else
                        switch (c) {
                        case '+':
                                return 62;
                        case '/':
                                return 63;
                        case '=':
                                return 0;
                        default:
                                throw new RuntimeException("unexpected code: " + c);
                        }
        }

        /**
         * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned.
         */

        public static byte[] decode(String s) {

                ByteArrayOutputStream bos = new ByteArrayOutputStream();
                try {
                        decode(s, bos);
                } catch (IOException e) {
                        throw new RuntimeException();
                }
                byte[] decodedBytes = bos.toByteArray();
                try {
                        bos.close();
                        bos = null;
                } catch (IOException ex) {
                        System.err.println("Error while decoding BASE64: " + ex.toString());
                }
                return decodedBytes;
        }

        private static void decode(String s, OutputStream os) throws IOException {
                int i = 0;

                int len = s.length();

                while (true) {
                        while (i < len && s.charAt(i) <= ' ')
                                i++;

                        if (i == len)
                                break;

                        int tri = (decode(s.charAt(i)) << 18) + (decode(s.charAt(i + 1)) << 12) + (decode(s.charAt(i + 2)) << 6) + (decode(s.charAt(i + 3)));

                        os.write((tri >> 16) & 255);
                        if (s.charAt(i + 2) == '=')
                                break;
                        os.write((tri >> 8) & 255);
                        if (s.charAt(i + 3) == '=')
                                break;
                        os.write(tri & 255);

                        i += 4;
                }
        }
}
